Organization and Expression of a Cluster of Drosophila Cuticle Genes

Year: 1983 DOI: 10.7907/mfee-te69
A 50 kb DNA segment of the Drosophila genome has been cloned and characterized. This segment lies at chromosomal location 44D and contains two small gene families. One family is comprised of four related cuticle genes clustered within 7.9 kb of DNA. The four genes encode four of the five major third instar larval cuticle proteins. These cuticle genes are coordinately expressed in the integument of third instar larvae, and they are not abundantly expressed in other developmental stages. A fifth cuticle-like gene lies within this gene cluster. It is judged to be a pseudogene, because several features of its structure and the absence of transcripts suggest that it is nonfunctional. Sequence comparisons indicate it arose by an unequal crossing over event involving two closely related and adjacent cuticle genes.

Eleven kb away from the cuticle gene cluster lies another gene family. This family is comprised of three genes that are 55-60% homologous in DNA sequence and clustered within 8 kb of DNA. The three genes are expressed together in larval stages and adults but show a different pattern of developmental expression from the third instar larval cuticle protein genes. Thus two small gene families can lie adjacent on the chromosome and exhibit different patterns of developmental expression, even though individual genes within a clustered family are coordinately expressed.

Additionally, a Drosophila strain has been studied which fails to synthesize one of the cuticle proteins. A molecular characterization of this strain is reported, which includes the finding of a transposable element in the promoter region of the unexpressed gene.